Digital terrain maps of the earth are available from various sources. For example, the Shuttle Radar Topography Mission (SRTM) is a joint project between the National Geospatial-Intelligence Agency (NGA) and the National Aeronautics and Space Administration (NASA). The objective of the SRTM is to produce digital topographic data for much of the earth's land surface using interferometric synthetic aperture radar. The digital topographic data can be formatted as height above mean sea level for each given latitude and longitude. While the digital topographic data of the earth produced by the SRTM is non-classified and publicly-releasable, digital terrain maps of the earth are available or can be generated from other non-classified and classified sources.
Automatic target recognition (ATR) techniques are known that actively identify targets such as moving and/or stationary aircraft, ships, motor vehicles, etc. These techniques use a transmitter to emit radio waves, which are reflected by a target, and a receiver to detect the reflected radio waves. By analyzing the detected radio waves, the identity of the target can be automatically determined.